Crank mechanisms are known furrow opener providing power to rotate a member, for example, pedals on bicycles. The pedals are conventionally attached to a circular sprocket to drive a chain to drive the bicycle wheel and provide propulsion. Typically the rider pushes down once the pedal reaches the top of its cycle to provide the force required to rotate the sprocket, and once the pedal reaches the bottom of the cycle no more force can be applied to rotate the sprocket. Then the opposite foot pushes down on the opposite pedal to provide the required force.
The rider's foot follows a circular path as the bicycle travels and the sprocket revolves. Only the force components that are tangential to the circular path at any given point on the cycle act in the direction required to rotate the sprocket. At a location 90° forward from the top of the pedal cycle, the downward force of the rider's foot is all going toward rotating the sprocket, however at all other points in the cycle only a portion of the downward force is in the proper direction to rotate the sprocket.